If you're using one of the few latest versions, the easiest thing to do is to open up that Gain block's parameters and right-click the text box where Rr is entered. This will give you two options to "open" or "explore" the variable.
This option is smart enough to figure out the location of the variable, which could be the base workspace, model workspace, a data dictionary, or a local variable in a masked subsystem.
If you don't have that option because you're on an older version, you can try right-clicking the Gain block and selecting "Find Referenced Variables" from the context menu. This will, for the most part, be equivalent to selecting that "explore" option; it will also open the Model Explorer.
- Sebastian
